Method of and apparatus for electrically producing sound



1,64o;141 Aug. 23, 1927. T BODDE METHOD OF AND APPARATUS FOR ELECTRICALLY PRODUCING SOUND Original Filed July 5. 1924 i7 Mm J'of 3 E U o. E c

X Gousss INVENTOR Theodore B dde ATTORNEY Patented Aug. 23, 1927.

UNITED STATES 1,640,141 PATENT OFFICE.

THEODORE IBOIDDE, OF NIAGARA FALLS, NEW YORK.

METHOD OF AND APPARATUS FOR EL EGTRICALLY PRODUCING SOUND.

Application filed m 5, 1924, Serial No. 724,379. Renewed January 7, 1927,

This invention relates to a method of and apparatus for electrically producing sound, and more particularly to a method of and apparatus for transforming sound waves or impulses into corresponding current pulsations or impulses by the action of a magnetically controlled electron discharge device.

As is well known, the electron stream or current between the electrodes of a vacuum tube or electron discharge devi e may be controlled by means of a magneti field; and in the action of these magneticalh controlled devices, if a constant voltage is impressed between the cathode and anode, the current that flows through the tube, that is, the electron stream that discharges from the cathode and impinges on the anode, while unaffected by a magnetic field having a strength less than a certain critical value, is reduced to zero if the magnetic field is increased beyond that value; and thus by changing the strength of the magnetic field to magnitudes below or above a critical amount, the electron stream or current across the electrodes and hence the current in a working circuit connected to the electrodes may be respectively established or extinguished.

The magnetically controlled electron tube, or magnetron as itis termed, in one of its most efficient forms comprises a vacuous ves,--

sel of cylindrical configuration provided with a linearly disposed filament which when heated to incandescence emits an electron stream which impinges upon acylindrical plate or anode symmetrically surrounding the cathode, the stream being controlled by means of a magnetic field which may be pro duced by an energized'solenoid or coil surrounding the tube or vessel. The paths of movement of the electrons projected from the cathode are found to be influenced by the magnetic field, the paths being bent or curved by the magnetic field; and the degree of curvature imparted to the paths varies with the strength of the magnetic field.

WVhen the field is below a critical value, the

electron paths although curved still intersect the cylindrical anode, and since the electrons impinge on the anode, the current through the tube remains unaffected. When however the magnetic field exceeds the critical value, the electron paths are bent sufficiently to prevent the electrons from reaching the anode, and since the electrons do not impinge thereon, no current flows across the electrodes and the current in the working c1rcu1t connected to the electrodes is accordingly extinguished.

I have discovered, as is disclosed in my copending application Ser. No. 613,273, filed Jan. 17, 1923, that this phenomenon or property of the magnetic control of the electron emission of the tube or device may be utilized for effecting the transformation of sound vibrations or impulses'into corresponding electrical impulses for sound product1on and transmission, and more particularly that when the controlling magnetic field is such as to produc an I electron emission which moves substantially tangentially to the anode, a relative vibration between the cathode and the anode electrodes in response to sound impulses will sensitively produce corresponding variations in the electron stream impinging upon or touching the anode, and hence corresponding current varlations in a working circuit connected to the anodeand cathode.

In my copending application referred to, I disclose a construction whereby vibration of the electron tube structure as a Whole is made effective for producing thedesired relative motion between the electrodes. I have found, however, that improved results may be obtained by reducing the inertia of the parts set in motion by the sound impulses, and more particularly that bymak in the cathode the vibratable element, the device is rendered more sensitive to sound impulses and any distortion of the reproduced sound is minimized. The provision of an improved method and electron discharge apparatus for transforming the sound impulses into electrical impulses in which the substantially inertialess cathode is set into vibration in correspondence with the sound impulses is a prime desideratum of my present invention. a

To the accomplishment of the foregoing and such other objects as may hereinafter appear, my invention consists in the elements and their relation one to the other, as hereinafter particularly described and sought to be defined in the claims; reference being had to the accompanying drawings which show a preferred embodiment of my invention, and in which:

Fig. 1 is a view showing my invention applied to a transmitter,

Fig. 2 is a view of a modification,

Fig. 3 is a graphical view showing the electrical characteristics of the magnetron and the manner of adjusting the magnetic field thereof, and

Fig. 4 is a diagrammatic View depicting the principles or theory underlying the invention.

Referring now more in detail to the drawings and more particularly to Fig. 1 thereof, the magnetically controlled devlce or magnetron generally designated as M is shown to comprise the vacuous vessel or tube 10 provided with the cathode in the form of a strai ht or linear filament 11 arranged axial- 1y 0% the tube, and an anode 12, the said anode comprising a section or portion of a surface of a cylinder as will be detailed further hereinafter arranged in circular symmetry with'the cathode 11, the filament being provided with the sealed terminal 13 and the terminal 14 and the anode bein provided with the sealed terminal 15; and encircling the tube 10 symmetrically with thecathode and anode there is provided the solenoid 1 6 for producing a controlling magnetic field.

For heating the filament to incandescence a closed circuit is provided which includes the battery 17, the opposite poles of which are connected to the filament terminals 13 and 14 by means of the conductors 18, 19, 20 and 21. As is well known, upon heating the filament 11 by means of this closed circuit, there will be an emission of electrons from the filament 11 to the anode 12, and upon closing a working circuit connected to the anode and cathode a current will be established therethrough.

For energizing the solenoid 16, the same may be connected to a source of current which may be the battery 17 by means of a circuit comprising the conductor 22, the coil of solenoid 16, conductor 23, rheostat 24 and conductor 19, the rheostat being employed for predeterminin the degree of energization of the solenoicf and hence the magnitude of the magnetic field.

If the electron discharge device be subjected to a ma netic field normal or at right angles to the electron paths and below a predetermined amount, the emission of the electrons from the cathode and the impinging of these electrons on the anode of. the device will be uninterrupted and unhindered, and if the tube be subjected to a magnetic field beyond such predetermined amount, the electrons will be diverted and prevented from reaching the anode, result ing in an opening of the tube circuit and the opening of the working circuit controlled thereby. The graphical representation of this phenomenon is shown in Fig. 3, in which the strength of the magnetic field is represented by the abscissae, and the strength of the current flowing between the cathode and anode is represented by the ordinates of the graph. If the magnetizin influence is less than the line represente as CD, the current in the working circuit will be a maximum represented by the line XC. If, however, the magnetization passes the critical point D, the current in the working circuit ecreases and rapidly diminishes to a minimum as the magnetic field approaches the value XE, the change along the curve DE being more or less abrupt as the parts of the magnetron are more or less symmetrical in arrangement. Now if, in stead of varying the magnetic field, the magnetic field is fixed at a value such that the electron stream moves substantially tangentially to the anode 12 and a relative vibration between the cathode l1 and anode 12 is pr0duced,.there will be obtained variations in the electron stream reaching the anode, which variations are proportional in magnitude or amplitude and in frequency to the relative vibrations between the anode and cathode. By connecting across the electrodes a receiving or working circuit which may include a receiver 25, the conductor 26, the battery 27, conductor 28 connected to the anode 12, conductor 29 and conductor 21 connected to the cathode electrode 1 1, it will be apparent that the variations in the electron stream will produce corresponding sound producing variations .in the current of the working or receiving circuit.

That the change in the electric current or stream varies proportionally with the impressed mechanlcal vibrations of the cathode or filament will appear from a consideration of Fig. 4 of the drawings. In this figure I show in diagrammatic fashion the underlying theory of the invention, and I desire it to be understood that although this theory I believe to be properly explanatory of the phenomenon or the behaviour of the apparatus, the theory is presented by wa of explanation only, and not by way 0 limitation. When the solenoid 16 is energized to produce a magnetic field having a. value at or about the critical value as represented for example by the asterisk on .the curve represented in Fig. 3, the current in the tube is at the transition point, and the average electron path may be represented by the curve a: (Fig. the electron ath being tangent to the anode 12. This, owcver, is only the average path, and due to such factors as the physical dimension of the filament. the lack of complete symmetry of the parts, etc, the electrons are projected from the cathode in a plurality of proximate paths such for example as the paths m, y and 2, the electrons in the path 2 impinging: on the anode, and the electrons in the path 3/ circling about in the closed path..as shown, without touching the anode. When the cathode is vibrated, however, it will be evident that more Or less of the electrons reach the anode acthe cathode occupies the position 11", noneof the electrons in the paths (l7, 3/ and 2 will touch the anode. It will therefore beevident that the total electron stream emanat ing from the filament and impinging against the cylindrical anode surface varies progressively with and in proportion to the vibratory motion that may be imparted to the filament 11.

For vibrating the substantially inertialess filament 11, the terminal 13 may be coiled as shown at 30, and the terminal 14 may comprise a short rigid metal rod which passes through the center of and is soldered air-tight to a copper or phosphor bronze membrane 31, this membrane being sealed air-tight to the glass of the magnetron tube 10 at 32 in'a. manner well known to those skilled in the art. The membrane 31 is preferably about one inch in diameter, and

has a thickness of about 0.010 inches. With this construction it will be apparent that the rod terminal 14 forms a lever with its fulcrum at the membrane 31. so that the rod-lever will be set into vibration when sound waves moving in the direction of the arrows shown in the figure impinge upon a disk or diaphragm 33 connected or fixed to the outer end of the rod 14. The vibratory impulses produced at the outer end of the rod-lever will be reproduced in the inverse direction at the inner end of the rod, and will be transmited to the filament 11, as will be obvious.

Referring now to Fig. 2 of the drawings. I show a modified form of magnetron construction in which longitudinal vibrations are imparted to the rod terminal in lieu of the transverse vibrations incident to the structure shown in F ig.. 1 of the drawings. In Fig. 2 the magnetron tube comprises an envelop or vessel 10 having the linearly arranged filament 11' and the symmetrically arranged cylindrical anode 12', one terminal of the filament being sealed as at 13' and the other terminal comprising the rod 14 arranged substantially normal to the filament 11, the said rod being soldered air-tight to the membrane 31 which is arranged in a plane parallel to the axis of the magnetron tube so that sound impulses impinging upon the diaphragm or disk 33 and moving in the direction as indicated by the arrow will produce longitudinal vibrations in the rod 14' and will correspondingly produce the desired movement of the filament 11' for varying the touching distance between the body of the electron stream and the anode 12'.

The anode 12 or 12 is a section or a part of a cylinder,.and more particularly a cylinder with one side cut away, and in the preferred form comprises a quadrant of a cylinder. The cylindrical anode, as distinguished from known magnetrons, is cut away on one side for the reason that if a full cylinder is employed, any variation in the electron ourrent on one side produced by the vibrations would be neutralized or compensated for by an equal and opposite variation on the oppos te side, roducing a net result of no var ation in t e working circuit. With one side of the anode, however, removed, the electron stream variations on one side of the cylinder produces the current in the workmg circult as desired.

The use and operation of the apparatus and the practice of the method will in the mam be fully apparent from the above detailed description thereof. It will be further apparent that although I have shown my inventlon applied to atransmitter wherein the filament is set directly into vibration 1n response to sound impulses, that this apphcation of the invention has been given merely by way of example, and that other applications will be obvious to those skilled in the art. For example, the magnetron .may be subjected to vibrations of the mechanical vibrating system such as is employed in phonograph sound reproduction for the transmission of speech. It will be further seen that with the provision of the apparatus described, an extremely sensitive transmitter is obtained, the moving element being substantially inertialess and the reion produced sound being free from unavoidthe structure disclosed without dearting' from the spirit of the invention, de ned in the following claims.

I claim:'

1. The method of transforming sound impulses into corresponding electrical impulses which consists in subjecting the electron stream of an electron discharge device-to a magnetic field such that the electron stream emanating from the cathode of the device is caused to move substantially tangentially to the anode of the device and in setting up vibrations of the cathode relatively to the anode responsive to sound impulses whereby variations in the electron stream im inging upon or touching the anode are prod iiced in correspondence with the sound impulses.

2. The method of transforming sound impulses into corresponding electrical impulses which consists in producing in an electron discharge device a curved electron stream moving from the cathode of the device to an ting up vibrations of the cathode relatively to the anode responsive to sound impulses whereby variations in the electron stream impingingupon or touching the electrode are produced in correspondence with the sound impulses.

3. The method of transforming sound impulses into corresponding electrical impulses which consists in subjecting the electron stream moving from the cathode to the anode of an electron discharge device to a magnetic field Which is normal to the paths of the electrons and which is of such magnitude as to cause the electron stream to move substantially tangentially to the anode and in setting up vibrations of the cathode relatively to the anode responsive to sound impulses whereby variations in the electron stream impinging upon or touching the anode are produced in correspondence with the sound impulses.

t. The method of transforming sound impulses into corresponding electrical impulses which consists in vibrating the cathode of an electron discharge device relatively to the anode in response to sound impulses to vary the condition of the electron stream emanating from the cathode and moving to the anode.

5. An apparatus for producing sound by variations of an electrical current compris ing an electron discharge device having a.

cathode and an anode, means for causing the electron stream emanating from the cathode to move substantially tangentially to the anode and means for eiiecting a vibration of the cathode relatively to the anode responsive to sound impulses for producing variations in the electron stream impinging upon or touching the anode in correspondence with the sound impulses.

an apparatus for producing sound by variations of an electrical current comprising an electron discharge device having a cathode and an anode, means for curving the stream of electrons emanating from the cathode, the surface of the anode being arranged tangent to said stream, and means for vibrating the cathode for varying the touching distance between the body of the electron stream and the anode surface.

7. An apparatus for producing sound .by'

and means for efiecting a vibration of the cathode relatively to the anode responsive to sound impulses for producing variations in the electron stream impinging upon or touch ing the anode in correspondence with the sound impulses.

8. An apparatus for producing sound by variations of an electrical current comprising an electron discharge device having a cathode and an anode, means for producing a magnetic field which is normal to the paths of the electrons emanating from the cathode and which is of such a magnitude as to cause the electron stream to move substantially tangentially to the anode and means for effecting a vibration of the cathode relatively to the anode responsive to sound impulses for producing variations in the electron stream impinging upon or touching the anode in correspondence with the sound impulses.

9. An apparatus for producing sound by variations of an electrical current comprising an electron discharge device having a cathode, an anode and a means producing an electron discharge controlling magnetic field which is'at or about the critical point, and means for effecting a vibration of the cathode relatively to the anode to produce variations in the electron stream impinging on the anode.

10. An apparatus for producing sound by variations of an electrical current comprising an electron discharge device having a cathode and anode and means for vibrating the cathode relatively to the anode for varying the condition of the electron stream cn'ianating from the cathode and moving to the anode.

Signed at Niagara Falls, in the county of Niagara and State of NeW-York,-this th day of June A. D. 1924.

THEODORE BODDE.

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